We investigated vibrational energy relaxations of S 1 perylene at an excess energy of ca. 2800 cm -1 in several ketone solvents by femtosecond time-resolved fluorescence measurements.Temporal evolution of fluorescence emissions occurs on the following distinct timescales: 70 ~ 330 fs, 0.6 ~ 1.1 ps and 1.8 ~ 4.9 ps. The latter two was assigned to the intramolecular vibrational redistribution (IVR), and to the solvent-assisted IVR (SA-IVR), respectively. In SA-IVR, intramolecular vibrational couplings are affected by elastic or quasi-elastic interactions between solute and solvents. Solvent dependence of the SA-IVR rates can be explained qualitatively by the tier V-V coupling mechanism.

Vibrational energy relaxations of S 1 perylene and S 1 12-(3-perylenyl)dodecanoic acid (PD) in 2-methyltetrahydrofuran at room temperature were investigated by using a Franck-Condon analysis of femtosecond time-resolved fluorescence spectra. Vibrational energy relaxation from |2〉, V′ ) 2 level of ν 7 mode, occurs not only via successive route, |2〉 f |1〉 followed by |1〉 f |0〉, but also via direct route, |2〉 f |0〉. The vibrational energy relaxation times were obtained as 2.7 ps for |2〉 f |1〉, 1.8 ps for |1〉 f |0〉, and 700 fs for |2〉 f |0〉 in perylene and 1.9 ps for |2〉 f |1〉, 1.2 ps for |1〉 f |0〉, and 500 fs for |2〉 f |0〉 in PD. An average-matrix-element treatment proposed by Fourmann et al. (Chem. Phys. 1985, 92, 25) was employed to account for these relaxation times in the Fermi's golden rule. Two parameters of the average-matrix element were estimated to be V 0 ) 0.59 cm -1 and 0.46 < R < 0.55 in our analysis, which were in reasonable agreement with Fourmann's analysis, V 0 ) 0.65 cm -1 and R ) 0.3, for fluorescence spectra of perylene in supersonic jet. To discuss the energy flow in the ν 7 mode, transient vibrational temperatures were also calculated at each time. "Intramode" thermal equilibriums in the ν 7 mode both for perylene and for PD are not established while the vibrational temperature is higher than room temperature.

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We propose an implementation scheme for the continuous-time quantum walk using a diatomic molecule and an optical frequency comb. We show an analogy between the quantum walk and the cascade rotational transitions induced by the optical frequency comb whose frequency peaks are tuned to the pure rotational transitions in the molecule. The strategy to compensate for the centrifugal distortion of the real molecule is also demonstrated.

Dimethylanthracene (DMA), which exhibits almost no self-association in bulk organic solvents, forms a dimer and emits excimer-like fluorescence in a gamma-cyclodextrin nanocavity in a dilute aqueous solution. The 1Bb and 1La electronic transitions of the DMA dimer split by 2230 and 344 cm(-1), respectively, in a fluorescence excitation spectrum obtained with the excimer-like emission. From these energy splits, the structure of dimer in relation to a dielectric constant inside gamma-CD was discussed on the basis of atom-atom Lennard-Jones potential calculations including Coulombic interactions. Excitation relaxations of DMA in the presence of alpha-, beta-, and gamma-CDs in aqueous solutions were investigated by time-resolved fluorescence. The results suggest that both the hydrated and anhydrated species exist in the alpha- and gamma-CD complexes, while only the anhydrated species exists in the beta-CD complex.

No abstract

The ability to control molecular wavefunctions may lead to novel quantum technologies, such as bond-selective chemistry and quantum computing. [1][2][3] An understanding of the coherent-loss process is essential for the realization of these quantum technologies using quantum-interference (QI) effects in condensed media. Although the overwhelming majority of chemical reactions take place in solution, there have been very few experimental studies on the coherent reaction control of polyatomic molecules in condensed media, because of the rapid decoherence of wavefunctions. These fast quantumphase relaxations are thought to be caused by solute-solvent interactions. [4,5] Thus, an understanding of the roles of solvent molecules in the dephasing mechanism is strongly required. It is noted that the inhibition of dephasing is necessary for the development of coherent control techniques for more general reactions. Therefore, the protection of molecular wavefunctions from the surrounding environment becomes an important issue for the realization of quantum-control techniques in condensed phases. Here, we aimed to protect the quantum phase of a guest molecule by using the size-fit nanospace of a cyclodextrin nanocavity.Cyclodextrins (a-, b-, or g-CD), which are oligosaccharides with hydrophobic interiors and hydrophilic exteriors, are used as nanocavities. The ability of CDs to encapsulate organic and inorganic molecules in aqueous solution has led to intensive studies of their inclusion complexes.[6] We intuitively imagined that the confinement of a guest molecule within the CD nanocavity would reduce perturbations from the surrounding environment, which cause the decoherence. Several studies on CD complexes with aromatic compounds, performed using timeresolved spectroscopy, have been reported. [6][7][8][9][10][11][12][13] To our knowledge, however, no experiments have been reported on CD inclusion to suppress decoherence. As far as we know, this is the first report on the CD encapsulation effect that moderates the decoherence of the molecular wavefunction at room temperature.Herein, we report the moderation of electronic decoherence of perylene in g-CD at room temperature, as measured by an optical-phase-controlled pulse-pair quantum interferometer, [14][15][16][17][18][19][20][21][22][23] combined with spectral lineshape analysis. A method to induce QI of molecular wavefunctions by a pair of phaselocked pulses has been originally developed by Scherer et al. and successfully applied to I 2 molecules in the gas phase. [14] The QI technique was successfully applied to various systems, such as GaAs quantum dots, [15,16] ZnSe films, [17] the Rydberg atom, [18,19] Cl 2 in an Ar matrix, [20] I 2 in the gas phase, [21,22] and a microcrystalline powder of a linked anthracene dimer.[23] Figure 1 shows the steady-state fluorescence and fluorescence-excitation spectra of perylene in both a g-CD aqueous solution and a tetrahydrofuran (THF) solution. Because of the low solubility of perylene in water (ca. 1.6 10 À9 m), [24] we could n...

We propose a strategy of isotope-selective ionization for a binary mixture of isotopologues of homonuclear diatomic molecules, utilizing field-free alignment with a train of femtosecond laser pulses. Field-free alignment can be achieved simultaneously for two isotopologues consisting of two atoms with the same atomic mass number α or β ( α X 2 and β X 2 ), utilizing a pulse train with their time interval of T rev com = βT rev α = αT rev β , where T rev α and T rev β are the rotational revival times of the isotopologues. We demonstrate experimentally that a train of four alignment pulses with their interval of T rev com (α = 14, β = 15) creates transiently aligned 14 N 2 and antialigned 15 N 2 just before T rev com /2 after the last alignment pulse and vice versa just after T rev com /2. Highly isotope-selective N 2 ionization is achieved at these timings with another femtosecond laser pulse, which induces the nonresonant multiphoton ionization with the cross section remarkably depending on the angle between the molecular axis and the laser-electric-field direction. The ion yield ratio I ( 15 N + 2 )/I ( 14 N + 2 ) ranges from 0.49 to 2.00, which is wider than the range obtained with a single alignment pulse [H. Akagi et al., Appl. Phys. B 109, 75 (2012)].